This invention relates generally to the preparation of higher alkyl aluminum compounds by an ethylene chain growth process and more specifically to the reduction of reactor fouling of tubular reactors used in such process.
Alpha-olefins are made in commercial quantities by a process initially developed in the fifties by Karl Ziegler and his co-workers. The so-called Ziegler process involves a chain growth reaction of triethyl aluminum ("TEA") and ethylene at temperatures in the range of 200.degree. F.-500.degree. F. and pressures in the range of 2000-5000 psig to yield a mixture of tri-C.sub.2-20+ alkyl aluminum having a Poisson alkyl distribution and C.sub.2-20 olefins. The ethylene is flashed from the reaction mixture for recycle and the light olefins through decene-1 can be distilled from the mixed aluminum alkyls since they have a normal boiling point below the lightest aluminum alkyl (viz. TEA). The mixed aluminum alkyls can be subjected to a displacement reaction with an alpha-olefin such as ethylene to produce mainly triethylaluminum and a mixture of C.sub.2 to C.sub.30 or higher .alpha.-olefins. The lighter olefins are removed by distillation and the distillation bottoms including triethylaluminum and some mixed olefins can be recycled to the chain growth process.
Examples of patents which disclose variations of the ethylene chain growth process are U.S. Pat. No. 2,863,896; U.S. Pat. No. 2,889,385; U.S. Pat. No. 2,906,794; U.S. Pat. No. 2,971,969; U.S. Pat. No. 3,180,881; U.S. Pat. No. 3,210,435; U.S. Pat. No. 3,227,773; U.S. Pat. No. 3,278,633; U.S. Pat. No. 3,352,940; U.S. Pat. No. 3,358,050; U.S. Pat. No. 3,359,292; U.S. Pat. No. 3,384,651; U.S. Pat. No. 3,391,219; U.S. Pat. No. 3,415,861; U.S. Pat. No. 3,458,594; U.S. Pat. No. 3,487,097; U.S. Pat. No. 3,663,647; U.S. Pat. No. 3,789,091; U.S. Pat. No. 4,314,090 and U.S. Pat. No. 4,935,569 where teachings are incorporated herein by reference.
The preparation of higher trialkyl aluminum compounds from an alkyl aluminum having fewer carbon atoms, such as triethylaluminum, by the controlled chain growth reaction with ethylene is highly exothermic. In one commercial scale chain growth process, a tubular coil reactor is surrounded by one or more shells filled with a fluid heat exchange medium such as an organic liquid or water which is circulated to remove heat from the reaction such that the desired reaction temperature, usually from about 90.degree. C. to 260.degree. C., is maintained. The reactor temperature is chosen to be high enough to maintain a practical rate of reaction and yet not so high as to cause a significant amount of undesirable side reactions such as decomposition of the aluminum alkyls. A problem associated with such reactor systems is that ethylene polymer deposits build up on the reactor walls which eventually reduce the flow through the reactor. When such deposits become so severe as to inhibit practical operation, the reactor must be shut down and cleaned. I have now discovered an improved chain growth process which greatly extends the reactor life between cleanings.